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Vol. 16-3 Chemistry Edition © 2016 Flinn Scientific

Supersaturated Solution

Sodium Acetate Demonstration

Continued on page 2

Introduction

Snap your fingers over a clear solution

and, presto, the solution instantaneously crystallizes. The flask can immediately be turned upside down without spilling a drop. The solution is easy to make and can be used over and over again.

Concepts

• Supersaturated solutions • Crystallization • Exothermic

Safety Precautions

Sodium acetate is slightly toxic by in

gestion, inhalation, and skin absorption.

Wear chemical splash goggles, chemical-

resistant gloves, and a chemical-resis tant apron. Wear heat-resistant gloves or use tongs when handling the hot flask. Please review current Safety Data

Sheets for additional safety, handling,

and disposal information.

Preparation

1. Weigh out of sodium acetate

trihydrate in a 500-mL Erlenmeyer flask.

2. Using a graduated cylinder, measure

out 30 mL of distilled water, and add it to the flask of sodium acetate trihydrate.

3. Heat the mixture on a hot plate

or over a Bunsen burner, stirring occasionally until all of the solid is dissolved. (This may take 15 minutes or so.) Make sure the sides of the flask are free of solid sodium acetate. To remove crystals from the sides of the flask, rinse them down with small squirts of water from the washing bottle.

Continued on page 4

What's Inside

Supersaturated Solution......1, 4

Laboratory Ventilation

.......1-2 Flinn PREP for AP Chemistry ..3

Molar Mass Mystery

..........5

Product Spotlight

.......... 6-7

Flinn Fax Bulletin Board

....... 8tended to provide guidelines on how to solve the problem of poor ventilation in your laboratories and preparation/stor-

age areas. We hope that you and your administration will follow these guide- lines in order to provide a safer working and learning environment for teachers and students at your school.

Fume Hoods

Fume hoods are an important feature in

any laboratory using hazardous chemi cals. Fume hoods provide a location for the dispensing and use of hazardous chemicals that are likely to form a vapor or aerosol that could be inhaled by the user of the chemical or others in the lab-One of the most important steps in main- taining a safe laboratory environment is to ensure that the laboratory is properly and adequately ventilated. Unfortunate ly, architects, engineers and adminis- trators who make the design decisions when planning a new or renovated labo- ratory frequently leave out plans for proper laboratory ventilation in an ef- fort to save money. Good ventilation is important to protect everyone who uses the laboratory from short-term exposure to toxic substances. Ventilation is equal- ly important for protecting the teacher from the hazardous effects of long-term exposure to hazardous chemical vapors, aerosols and fumes. This article is in

Laboratory Ventilation

Reducing Chemical Exposure

Materials (for each demonstration)

Graduated cylinder, 100-mL or 50-mL

Sodium acetate, trihydrate, CH

3 CO 2

Na•3H

2

O, Heat-resistant gloves or tongs

160 g Hot plate or Bunsen burner

Water, distilled or deionized, 30 mL Parafilm M

or 100-mL beaker, to cover the flask Balance Ring stand set-up, if using a Bunsen burner Flask, Erlenmeyer or Florence, 500-mL, Stirring rod, glass Borosilicate Glass Washing bottle filled with distilled water

See the Free Video at

www.flinnsci.com/supersaturated

SCIENTIFIC

oratory. It is a common misconception that fume hoods provide adequate room ventilation in a school science labora- tory. Fume hoods are not designed for room ventilation. Fume hoods are only designed to ventilate the activity taking place in the fume hood itself and to pre- vent the release of hazardous chemicals into the general laboratory environment.

When functioning properly, a fume

hood should have a face velocity of

80-120 feet per minute (fpm).

1 This is a measurement of the amount of air moving across the front opening of the hood and can be measured using a de vice called a velometer (Catalog No.

SE4055) available from Flinn Scientif

ic. In order to work efficiently, a fume hood should be located more than 10 feet from any doorway or window and should not be located near major traffic areas. Fume hoods should be checked periodically to make sure that they are working properly and efficiently.

The fume hood ductwork should be

checked annually to make sure that it is in good condition and venting directly to the out-of-doors, away from build- ing air intakes. Fume hoods should be checked using a velometer or a small smoke generator which will allow you to test the effectiveness of your hood as well as its exhaust location at the ex- terior of the building. Simply turning the fume hood on and hearing the mo- tor run does not constitute a thorough fume hood test.

A fume hood should never be used

as storage space for chemicals or other items. Doing so not only decreases the efficiency of the hood, but also creates an unsafe situation for the user(s) of the hood. When items are stored in the hood they will prevent proper airflow, which decreases the hood's efficiency.

Additionally, items stored in the hood

force the users to perform their tasks closer to the front of the hood, which in- creases the possibility that the products or fumes from their activity will enter the general laboratory environment.

Fume hoods generally function most

efficiently when used with the indi- vidual blower provided with the hood.

Connecting multiple fume hoods to

common ductwork and using a single, large blower is not recommended as the rate of air exhaust is usually insufficient to provide a face velocity in the accept able range. Also, ensuring the proper amount of draw from each hood is dif- ficult when using more than one hood at the same time.

Laboratory Ventilation - Continued from page 1

Laboratory Ventilation

Good laboratory ventilation is the sin

gle most important ingredient in main- taining a safe laboratory environment.

The ability to quickly provide a com

plete air change in science laboratories will greatly minimize the potential for chemical exposure. Good laboratory ventilation will allow teachers and ad- ministrators to feel safe and comfort- able in doing all of the experiments and activities needed to provide an out- standing laboratory experience for their students. Adequate ventilation will also decrease the risks of long-term expo- sure to chemicals for teachers and other laboratory personnel. Unfortunately, architects, engineers and administrators often get so concerned about conserv ing energy, money and HVAC (heating, ventilation and air-conditioning) costs, that they ignore the need for proper ventilation of the science laboratory.

It is up to the science teacher to ensure

that all key decision-makers are aware of the need for good ventilation.

So, how much ventilation is enough?

The OSHA Laboratory Standard 1910

states that "4 to 12 room air changes per hour is normally adequate general ventilation." 2

Air that is exhausted from

the laboratory should always be vented to the out-of-doors and should never be recirculated. This will prevent labora tory air from being drawn back into the school building. Ideally, the ventilation system should provide a minimum of six complete air changes per hour. 3

Six complete air changes per hour are

needed when conducting experiments that generate hazardous vapors or to re move particularly strong or long-lasting odors. An exchange rate of six or more air changes per hour can be most easily achieved using an auxiliary ventilation system such as a purge fan or ceiling ventilator. Whichever type is chosen,

the system must move a large enough volume of air in cubic feet per minute (CFM) to provide the desired rate of air exchange.

With any auxiliary ventilation system,

it may be necessary to open the labora tory doors in order to provide enough make-up air to allow the system to pro- vide the required air change. Make-up air is the air required from outside the room (for example, a hallway) to re place the air being removed from the laboratory by the ventilation system.

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